Digital electronic component which is protected against electrical-type analyses

ABSTRACT

This invention relates to a digital electronic component which is protected against electrical- and/or electromagnetic-type analyse). The inventive component comprises: a synchronous element ( 10 ) which is controlled by a clock (H); means ( 11, 12 ) of generating said clock (H), the frequency of which varies randomly between a minimum value and a maximum value for at least a given period of time; and means ( 13 ) of controlling the random nature of the frequency change of said clock (H).

TECHNICAL FIELD

The present invention concerns a digital electronic component that isprotected against electrical and/or electromagnetic type analyzes, moreparticularly in the field of the chip card.

STATE OF THE ART

The field of the invention is in the implementing in a digitalelectronic component, for example in a chip card, of mechanisms tocombat data extraction (usually with an encryption key) by means of ananalysis of the current consumption, or by analysis of the emittedelectromagnetic radiation. These analyzes are generally called SPA(“Simple Power Analysis”)/DPA (“Differential Power Analysis”) or SEMA(“Simple Electrical Magnetic Analysis”)/DEMA (“Differential ElectricalMagnetic Analysis”).

Using these analyzes it is possible to determine what the central unitof a chip card is doing, which data are being manipulated by the latter.It is possible thereby to access the single (or plurality of) secretkey(s) used for transmitting this data. Such an intrusion may be donewithout any risk, because it will not be possible to prove afterwardsthat it has happened since the component remains unaltered.

As described in the article of Paul Kocher, Joshua Jaffe and BenjaminJun entitled “Introduction to differential power analysis and relatedattack” (Internet site www.crytograhy.com, Cryptography Research, 1998),these methods of analysis may have important impacts, because they allowto extract secret keys used for encrypted communications. Furthermore,such attacks may be set up rapidly and implemented using easilyavailable equipment. The amount of time required to realize theseattacks depends on the type of attack (DPA, SPA) and varies as afunction of the considered component. An SPA attack may take a fewseconds for a component while a DPA attack may take many hours.

Nowadays digital electronics are minimally or not protected against suchelectrical or electromagnetic analyzes. Two families of attacks exist:the one is purely software, the other is purely hardware. In the case ofdata manipulated by the central unit of a chip card:

-   -   in the first family, one technical solution consists in        rendering the current consumption as random as possible, this        current consumption being linked the less possible to the data        manipulated by the central unit. This way it is possible to        randomize the sequence of the instructions, or render as random        as possible the data manipulated.    -   in the second family it is possible to:        -   either render the current as steady as possible so as to            make it very difficult to realize a link between the current            consumption and the instructions manipulated by the central            unit,        -   or randomize the current consumption so as to de-synchronize            two identical operations of the central unit.

The invention belongs in this second case.

A European patent application EP 1 113 386 describes a solution toprotect a chip card against such attacks. In this solution, twocondensators are embedded in the chip card such that at any time one ofthem is charged by an external power supply and the other is dischargedby activating the component of the chip card. The roles of the twocondensators rapidly alternate and the power supply is isolated from thecomponent of the chip card in the sense that analyzes of the currentconsumptions do not produce any information about the operation of thiscomponent.

The aim of the invention is to solve the problem described here above,by varying in a random fashion the speed of operation of a considereddigital electronic component, for example a chip card, such as to renderSPA/DPA and/or SEMA/DEMA analyzes difficult, and perhaps impossible.

SUMMARY OF THE INVENTION

The invention relates to a digital electronic component which isprotected against analyzes of the electrical and/or electromagnetic typecomprising a synchronous element driven by a clock, characterized inthat it comprises means for generating of this clock, the frequency ofwhich varies randomly between a minimum value and a maximum value duringat least a given time period, and means for controlling the randomnature of the frequency change of the clock.

The means for generating of a clock may comprise a random frequencyinstruction generator that commands a frequency generator.

The frequency generator may comprise at least two frequencysynthesizers, or PLL circuits (“Phase Locked Loop”), and means forswitching between these synthesizers, or circuits.

The synchronous element may be the central unit of a chip card, amemory, or a cabled synchronous function, for example of the FPGA type(“Field, Programmable Gate Arrays”) or ASIC type (“Application specificintegrated Circuit”).

The range of frequency variation must be as wide as possible to disturbat a maximum analyzes of DPA/SPA and DEMA/SEMA type. The consideredrandom is a real random, because in this case it is not a phase orfrequency shift of the clock, but a driven random frequency change. Bydisturbing the clock in this manner the current consumption of thesynchronous element is rendered random.

BRIEF DESCRIPTION OF THE DRAWINGS

The only Figure illustrates a digital electronic component that isprotected against attacks of the electrical and/or electromagnetic type.

DETAILLED DESCRIPTION OF PARTICULAR EMBODIMENTS

As illustrated in the Figure the digital electronic component that isprotected against attacks of the electrical and/or electromagnetic typeaccording to the invention, for example of a chip card, comprises:

-   -   a central unit 10 of this chip card,    -   a random frequency instruction generator 11,    -   a frequency generator 12 driven by this generator 10, that        provides to this central unit 10 a clock H, the frequency of        which varies in a random manner between a minimum value and a        maximum value,    -   a controller 13 that aims at measuring the frequency of the        clock H and verifying the real random operation of the frequency        change.

The frequency excursion of the clock H, which is as great as possible,is comprised between 1 Mhz and 100 Mhz.

In the example of embodiment illustrated in the Figure, the frequencygenerator 12 comprises at least two frequency synthesizers SF1 . . . SFncontrolled by signals provided from outputs 15 of the controller 13, anda multiplexing and synchronizing circuit 20 receiving the outputs F1. .. Fn of these synthesizers SF1 . . . SFn.

At the occurrence of a frequency change, before selecting one of thefrequencies at the output of the synthesizers SF1 . . . SFn by sending asignal SEL on the multiplexing and synchronizing circuit 20, thecontroller 13 verifies that there are no possible disturbances byanalyzing the signals received at its inputs 16.

The controller 13 may hence operate in the following manner:

-   -   request from the random frequency instruction generator 11 of a        new value,    -   value provided by this generator 11 to the controller 13,    -   verifying by the controller 13 of the random nature of this        value as compared to previous values,    -   sending of this value to the synthesizers SF1 . . . SFn.

The invention allows to randomize the operation of the central unit,that performs the calculations, and to give an appearance of randomcurrent consumption. Analyzes SPA/DPA and/or SEMA/DEMA are difficult,perhaps impossible to make because they require a considerable increaseof the number of current analyzes.

The invention allows not to modify the central unit as such, and tooperate it in its own range of frequencies.

The ability of the invention to protect itself depends from the randomfrequency instruction generator and from the frequency change cycledepending on the length of an instruction cycle of the central unit.

In an advantageous embodiment, the controller may be driven by thecentral unit.

In an alternative operation it is possible to activate the randomfrequency change of the clock H according to the invention only during agiven time period in cases considered as critical.

1. A digital electronic component that is protected against analyzes ofthe electrical and electromagnetic type comprising a synchronous elementdriven by a clock, wherein the clock comprises a random frequencyinstruction generator and wherein the frequency of the clock varies in arandom manner between a minimum value and a maximum value during atleast a given time period; and wherein the frequency generator comprisesat least at least two PLL circuits as frequency synthesizers and meansfor switching from a first frequency to a second frequency by switchingfrom a first PLL circuit to a second PLL circuit.
 2. The componentaccording to claim 1, in which the synchronous element is the centralunit of a chip card.
 3. The component according to claim 2, in which thecontroller is driven by the central unit.
 4. The component according toclaim 1, in which the synchronous element is a memory.
 5. The componentaccording to claim 1, in which the synchronous element is a cabledsynchronous function.
 6. The component according to claim 1, in whichthe frequency excursion of the clock is between 1 Mhz and 100 Mhz. 7.The component according to claim 1, further comprising means forcontrolling the random manner of the clock.